Don’t Expect Too Much of Soy

Women at menopause can begin losing bone and mental acuity. At the same time, their risk of heart disease increases. Although several lines of research had suggested that these problems might be diminished by replacing the hormones women lose at menopause, more recent studies have shown that the pharmaceutical supplements pose their own substantial risks of stroke, dementia (SN: 5/31/03, p. 341: available to subscribers at Flawed Therapy: Hormone replacement takes more hits), and breast cancer (SN: 7/27/02, p. 61: Hormone therapy falls out of favor).

For years, some women have been substituting soy and other plant sources of estrogenic compounds for the now-shunned hormone-replacement therapy (HRT). The rationale: Though far weaker than real estrogens or the HRT drugs, the natural alternatives could still elicit some estrogen action and thus might preserve the hormones’ antiaging benefits without triggering HRT’s risks.

Two large, new studies in European women now dampen hopes that such dietary alternatives will fill the bill.

However, these studies don’t quash soy’s prospects altogether. Several studies, especially in animals, continue to generate data indicating that plants with estrogenic properties offer at least limited protection from the ravages of aging. One of the latest studies suggests that soy might even offer mental benefits for aging men.

First, the bad news

Epidemiologist Sanne Kreijkamp-Kaspers and her colleagues at the University of Utrecht’s medical center recruited some 200 healthy postmenopausal women to take part in a yearlong trial. The women, ages 60 to 75, received a vitamin-enriched powder containing either soy or milk protein to add to their diet each day. A certified dietician provided recipes and other suggestions for each woman on how to incorporate the 25 grams of powder into her menu.

Neither the physicians who were directing the trial nor the volunteers taking part knew which protein a woman had been randomly assigned to take.

In fact, Kreijkamp-Kaspers notes, the powders were designed to taste similarly. To test how well the study succeeded in blinding the volunteers to their treatment, her team asked a cross section of women to guess which protein they were getting. It turned out that an equal number from each group guessed rightly and wrongly, confirming that the women really couldn’t distinguish the proteins by taste, says Kreijkamp-Kaspers.

Quarterly, the doctors had the women return to the medical center to provide blood samples, get their vital signs recorded, and to report any possible side effects associated with taking the supplements. During the year, slightly under one-quarter of the volunteers in each group dropped out.

Of those who remained, the researchers could find no major benefit associated with the soy supplementation, they report in the July 7 Journal of the American Medical Association.

For instance, both groups experienced a loss of bone during the year. Declines were comparable in both the total hip and lumbar spine, although the soy group did show 1.3 percent less bone loss in a portion of the hip known as the intertrochanter region. This is an area especially vulnerable to osteoporotic fractures in the elderly.

Heart disease is the leading cause of death in older women, and the risk of the disease increases dramatically beginning at menopause, when cholesterol concentrations tend to climb. After the year of taking one or the other supplement, blood concentrations of low-density-lipoprotein (LDL) cholesterol, the so-called bad cholesterol, in the two groups were the same. Nor were there statistical differences in the groups’ performances on tests of memory and other mental tasks.

In general, Kreijkamp-Kaspers told Science News Online, the findings were a big surprise, because her team had expected to find some substantial benefit attributable to the soy. Many previous studies of soy supplementation in people had indicated benefits in bone density, heart risks, and brain health. The new study, the largest and best-controlled trial to date, was expected to resolve which aspects of aging were most likely to be prevented or slowed by soy.

Kreijkamp-Kaspers now wonders whether her group’s inability to find any clear-cut benefits from soy means that the recruits simply started supplementation too long after menopause. As she puts it: “Perhaps after the damage is done, it’s too late to reverse.” Her team is planning a follow-up in which they’ll commence supplementation around the time that a woman’s production of estrogen begins to wane.

In a related study, Charlotte Atkinson of the Institute of Public Health in Cambridge, England, and her coworkers supplemented women’s diets for a year with plant estrogens from red clover. The research team recruited 205 women ages 49 to 65, randomly assigning half to take daily tablets that contained the clover compounds, and gave the remainder look-alike tablets with no hormonal ingredient. Neither the 177 women who completed the study nor the researchers knew who was getting which pills until after the trial was over.

As in the soy-powder trial, the two tablets produced no difference in blood concentrations of cholesterol. In addition, no difference emerged in blood-clotting factors or blood pressure.

“In conclusion,” Atkinson’s team reports in the July Journal of Nutrition, “there were no significant effects of the [dietary] supplement.”

Elsewhere—hints of promise

Another study in the same journal, however, indicates that it may be too early to eliminate plant-derived estrogens (phytoestrogens) from the arsenal for battling chronic disease and aging.

A Korean team of scientists found that giving elderly male rats soy phytoestrogens for 16 weeks reduced the normal age-related loss of nerve cells in various parts of the brain. Moreover, it improved mental performance by the animals, as measured by their performance in a water maze. “In the near future,” says study leader Hyong Joo Lee of Seoul National University, “we will study the effects of soy [phytoestrogens] on cognitive function in females.”

Lee and his colleagues suspect the phytoestrogens in their supplements—genistein, daidzein, and glycitein—work by ratcheting up the activity of brain cells that depend on the nerve-signaling compound choline. Certainly, their analyses of brain tissue showed that the soy-supplemented animals had dramatically higher activity than the control animals in those areas that are especially dependent on choline for signal processing and memory building.

If true, that would explain a lot. Indeed, a new memory-fortifying dietary supplement described by Massachusetts Institute of Technology researchers last year relies on a form of choline as its key ingredient (Science News Online: Food for Thought, 11/22/03: A Forget-Me-Not Dietary Supplement?). Choline, a building block of every cell, is itself being explored as an antiaging supplement.